1. Field of the Invention
This invention relates to novel hot-melt adhesive compositions. The invention provides thermoplastic hot-melt adhesive compositions which are capable of adhering articles at low temperatures (about 100.degree. to about 130.degree. C.) and imparting high bond strength to honeycombs by fully penetrating thereinto or forming fillets thereon. The present compositions also give high bond strength to metal or plywood materials and have outstanding resistance to water, moisture and heat (at about 80.degree. to about 90.degree.C.).
2. Description of the Prior Art
Hot-melt adhesives are useful to various articles including those of honeycomb structure which have found wide application, typically for use as doors, panels, partitions, etc.
These articles are prepared generally by spraying a rubber or epoxy resin adhesive of the solvent type to the opposite sides of a honeycomb core material and to one surface of each of opposite metal or plywood facings, holding the resulting sandwich assembly between hot pressing means for a given period of time for thermal activation of the adhesive and allowing the assembly to stand under predetermined pressure at room temperature for one day.
The method described is therefore inefficient and involves problems in that the solvent used produces adverse effects on the environment as well as on the human body. To overcome these problems, it has been proposed to use hot-melt adhesives of the solvent-free type, especially film-shaped adhesives which assure the highest production efficiency. Hot-melt adhesive films must fulfil the following requirements.
(1) For use in laminates of honeycomb structure faced for example with coated metal sheets, the adhesive must have good adhering properties at low temperatures, since the facing sheets need to be adhered to the honeycomb usually at 100.degree. to 130.degree. C. to avoid the thermal degradation of the coating. PA1 (2) The adhesive must be capable of fully penetrating into the honeycomb or forming fillets thereon to provide a strong bond between the honeycomb and a metal or plywood facing. PA1 (3) Despite the good adhering properties required at low temperatures, the adhesive must give satisfactory heat resistance to the resulting product which is likely to be heated to about 80.degree. to about 90.degree. C. as when exposed directly to the sunlight.
The known plastic hot-melt adhesive films nevertheless still fail to meet these requirements.